Split Screen Resolution Problem (Game Engine)
I have that problem too. Try making the focal area larger, although it may be an issue with having two cameras.

Although, the snarky answer would be to restore down the game window.

Or you could do it like MarcClintDion commented. But really, make a note of the position of each camera, and slowly move them until you get the results you want.

Also, check if it's only going to fail with width. See if you can't stack the screens on top of each other, and see what effect that has on the width.